This invention relates to an improved brazing technique. Brazing is one of the general groups of welding processes, where welding is a method of joining metals by fusion or by solid-state processes. A weld is defined as the localized coalescence of metal wherein coalescence is produced by heating to suitable temperatures, with or without the application of pressure, and with or without the use of filler metal. Brazing involves the use of a filler metal having a lower melting point than that of the metals being joined. In brazing, coalescense is produced by heating. The non-ferrous filler metal used has a melting point below that of the metals being joined, so that upon heating the filler metal is distributed in the joint to be brazed by capillary attraction. Cleaning of the joints is essential for satisfactory brazing.
In brazing it is necessary to remove rust, grease, scale, etc., from the surfaces of the joint for proper distribution of the brazing material by capillary attraction. Joints are commonly cleaned chemically, such as with solvents and by electropolishing, and mechanically, such as with abraiding wheels, buffers, and sand blasting. The sand blasting consists of particles of hard granular material blown by a jet of compressed gas against a hard surface which it is desired to abrade. Certain types of joints are difficult to clean properly and require repeated attempts before a successful brazement is obtained. The problem of cleanliness becomes more critical when the joint to be brazed must be mechanically sound and leak tight. For example, joints formed between stainless steel components and thermocouples used diagnostically on reactors must be mechanically sound and leak tight to 2.times.10.sup.-9 std cc/sec of helium. Existing cleaning procedures cannot be used to obtain the required brazements.
Therefore, it is an object of the present invention to provide an improved brazing technique that achieves mechanically sound, leak tight joints.
It is another object of the present invention to provide an improved method of cleaning and preparing joint surfaces for brazing.
It is yet another object of the present invention to provide a method of obtaining mechanically sound, leak tight joints between stainless steel components.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.